Reducing power consumption is becoming a critical issue in designing mobile devices such as computers and telephone handsets. The issue of low power consumption design relates among other things to Wireless Local Area Networks (WLANs) as many of the network's nodes are placed on mobile stations.
Generally, communication systems are configured so that internal losses in the transmitter and the receiver will enable the system to meet required performance. In particular, in a packet based system, such as the IEEE 802.11x family, the transmitter sets its modes (including power, constellation, coding rate, number of transmitting antennas) according to some sort of channel estimation based on previous packets sent through the network. The above-mentioned modes' setting is performed without an actual knowledge of the present channel conditions (such as fading). As a result, in order to ensure high probability of correct decoding of the packet, the transmitted signal parameters are typically designed for channel conditions much worse than the average expected channel conditions.
Consequently, for most packets the loss inflicted by the noise will be smaller than the noise assumed in design and so decoding will be conducted with significant margins so that the implementation losses in the receiver may be raised without significantly affecting total performance.
Similarly, different features of the receiver are designed to deal with factors such as out of signal-band noise, or high coupling between channels in a MIMO system. When these factors are not substantial, these receiver features may be taken off or used with reduced functionality or performance.
The result deriving from the above-mentioned conditions and constraints is that power management in wireless receivers is not efficient enough and a substantial amount of power may be saved for most of the received packets. The main problem is, that since the receiver has to be designed for low packet error rate, it almost always meets the worst-case scenario.
In some networks, particularly in wireless ones, the deviation in requirements for different packets is very large. Consequently, the average power consumption can be much lower than the worst-case one, and the potential in reducing the average power consumption is therefore substantial.
Several attempts have been made so far in order to deal with the above-mentioned power consumption challenge.
U.S. Pat. No. 6,693,953 teaches a method for reducing power consumption in a receiver based on reducing the power consumption in one of the receiver's modules, the analog to digital converter (ADC). Particularly, the ADC is configured to operate in a lower bit precision whenever the signal is of generally high quality.
U.S. Pat. No. 6,538,592 suggests an ADC having a multi stage structure, wherein some of the stages are not always activated and so power consumption is reduced.
U.S. Pat. No. 6,917,820 teaches a method for configuring the antenna sets of a receiver and a transmitter in a manner that reduces power consumption. In particular, by choosing a set of both transmission and receiving antennas from a larger number of existing antennas, power may be saved.